1. Field of the Invention
This invention relates to overbased additives for lubricant oils containing an organic molybdenum complex virtually insoluble in hydrocarbons.
2. Description of the Invention
The overbased additives are alkali metal or alkaline earth metal salts of organic acids rendered overbased by carbonation with carbon dioxide. The term overbased is used to denote the excess of alkali metal or alkaline earth metal relative to the stoichiometric amount necessary to neutralize the organic acid used.
The structure of the overbased additives is that of a colloidal dispersion in which the micelles contain the alkali metal or alkaline earth metal carbonate formed during the carbonation. The micelles are stabilized by the alkali metal or alkaline earth metal salts of organic acids which have a detergent effect.
The salts of organic acids used in the overbased additives are in general the sulphonates, the salicylates or the sulphurized phenolates described, respectively, in the U.S. Pat No. 4,604,219, EP-A 279,493 and FR 2,305,494.
These overbased additives are usable, in particular, in the lubricants used in internal combustion engines of the "petrol" type or of the "diesel" type.
Owing to their detergent and dispersant effect, they prevent the formation of lakes and varnish and keep in dispersion the soots resulting from the incomplete combustion of the fuel.
Another important function of these additives is the neutralization of acid compounds, such as the organic acids formed by oxidation of the oil and the acids formed during the combustion of the sulphur-containing products introduced by the fuels.
This neutralization function is particularly appreciated when using fuels rich in sulphur, such as the heavy fuels used in marine engines.
It is known, moreover, to use molybdenum-containing additives as friction-reducing agents in lubricants. The earliest product used was molybdenum bisulphide in the form of a stable dispersion.
To avoid the operations of grinding molybdenum bisulphide and bringing it into a stable dispersion, it was proposed to use oil-soluble organic molybdenum compounds which can be incorporated directly in the lubricants.
Amongst the oil-soluble molybdenum compounds, the dithiocarbamates (EP-A 205,165) and the molybdenum complexes with oxazoline (U.S. Pat. No. 4,176,073) may be mentioned. The molybdenum complexes with the compounds containing a basic nitrogen resulting from succinimides, amides, phosphonamides or Mannich bases are used in the sulphurized form (U.S. Pat. Nos. 4,263,152, 4,369,119, 4,395,343).
Molybdenum-containing overbased additives are also known. The molybdenum is incorporated in the form of an inorganic compound while (U.S. Pat. No. 4,601,837) or after (U.S. Pat. No. 3,496,105) rendering overbased.